It is now widely appreciate that cancer is a multistep process in which the full blown cancer phenotype emerges as increasingly aggressive cell populations replace less aggressive ones. Understanding this process, known as progression, is one of the most pressing problems in cancer biology. What is needed to understand the molecular basis of progression and its cellular consequences is a model in which cancer develops as a eries of histopathologically definable stages, a strategy to define these changes in molecular terms and ways to distinguish those changes which are essential to progression from those which merely accompany changes. The development of transgenic models of liver and kidney carcinogenesis would provide an opportunity to conduct such studies on a comparative basis. We have recently cloned and sequenced the 5' flanking region of the gamma- glutamyl transferase gene (gammaGT) and will use it to direct the expression of oncogenes to mouse liver and kidney and to study on a comparative basis tumor development in these organs. The gammaGT 5' flanking region has a liver-preferred and a kidney-preferred putative transcription start. In initial experiments the entire region will be used to drive the rasT24 oncogene or the SV40 T antigens. In subsequent experiments we plan to separate the promoters and derive transgenic mouse lines that develop liver or kidney tumors. Morphologic changes will be followed by histopathology (H & E, toluidine blue, reticulum, and alpha- fetoprotein staining). We will use standard classification schemes as a framework for our initial analysis of progression. To determine if there are tumors at other sites or metastases, complete autopsies will be performed and histopathology where appropriate. We will evaluate the integration of transoncogenes (gammaGT/rasT24; gammaGT/SV40Tag) and changes in transoncogene and resident oncogene (fos, jun, myc, neu/erbB-2, lca families) structure (rearrangement, amplification, deletion) in liver and kidney tumors by Southern and dot blotting. Similarly, changes in the expression (steady state RNA levels) of transoncogenes and resident oncogenes will be analyzed by northern blotting. by studying transgenic carcinogenesis on a comparative basis in liver and kidney we can begin to determine which changes are essential to cancer development, which are organ specific and which are adventitious. Thus, for example, we can look at the relative importance of individual resident oncogenes in liver and kidney carcinogenesis in animals carrying either rasT24 or SV40 T antigens or the relative importance or vascular invasion in transgenic liver and kidney cancer.